Gets the specified user by user name in a user pool as an administrator. Works on any user.
/// This exception is thrown when Amazon Cognito encounters an internal error.
///
/// This exception is thrown when the Amazon Cognito service encounters an invalid parameter.
///
/// This exception gets thrown when a user is not authorized.
///
/// This exception is thrown when the Amazon Cognito service cannot find the requested
/// resource.
///
/// This exception gets thrown when the user has made too many requests for a given operation.
///
/// This exception is thrown when a user is not found.
///
